Preventing a Pug From Eating Cat Poop

To protect their cat's litter box, the Science Buddies built this magnet door that keeps their dog out.

Cameron Coward
1 month agoAnimals / Sensors

If you own both a dog and a cat, you may have noticed a disturbingly common trend: many dogs like eating cat poop. That is, of course, pretty darn icky. Most solutions to this problem hinge on the fact that dogs tend to be larger than cats. But some cats are big and some dogs are very small, which is exactly the situation the Science Buddies found themselves in. Their pug loves cat poop and happens to be smaller than the cat that emits the poop, which is why they built this clever electronic contraption that prevents that consumption.

Like most pet owners in this situation, the Science Buddies attempted to secure the litter box of Trouble the cat behind a small cat door. But because Riley the pug is smaller than Trouble, she can easily fit through that door. Other popular solutions also failed, which forced the Science Buddies to turn to more innovative solutions. They determined that the best strategy would hiding the poop behind a motorized cat door that closes whenever Riley attempts to pass through.

We’ve seen similar projects that rely on RFID tags and even AI to recognize the unauthorized (or authorized) pet, but those technologies both come with major drawbacks. RFID has a very limited range, while AI requires more expensive hardware and is difficult to train. This solution is far more practical, as it utilizes affordable reed switches.

A reed switch toggles current flow when in the presence of a strong enough magnetic field. Such switches are very inexpensive and range is proportional to the strength of the magnetic field. In this case, that field comes from a permanent magnet on Riley’s collar. That’s pretty small, so it needs to get close to a reed switch to toggle it. For that reason, the Science Buddies put several reed switches along the bottom of the entry. When Riley tries to pass, the magnet on her collar with get close to touching at least one of them.

An Arduino Uno board monitors the reed switches. When at least one toggles, the Arduino knows that Riley is there and it closes the entry doors. Those doors are made of cardboard and are actuated by little hobby servo motors, so there isn’t any danger of them hurting Riley. But brute force isn’t her style, so they are enough to keep her out.

For now, at least, Trouble’s poop is safe from Riley’s voracious appetite.

Cameron Coward
Writer for Hackster News. Proud husband and dog dad. Maker and serial hobbyist. Check out my YouTube channel: Serial Hobbyism
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